1. Field of the Invention
The present invention relates to a fine wire of a gold alloy containing nickel for bonding semiconductor devices, to a method for its production, and to its use.
2. Background of the Invention
For contacting or bonding semiconductor devices, suitable wires, also known as bonding wires, must have good electrical properties and good mechanical strength values. The diameter of the wires can be approximately 10 to 200 .mu.m and is typically in the range of approximately 20 to 60 .mu.m; the diameter is selected to suit the intended purpose.
The bonding wires often comprise gold of high purity, or recently also gold alloys. The latter have the advantage of greater strength and, if they contain only a slight quantity of alloy formers, their electrical conductivity is reduced only slightly over pure gold.
For instance, the use of an alloy of gold and 0.001 to 0.1% of one or more rare earth metals, especially in the form of cerium mixed metal, or yttrium is known from German Patent DE 16 08 161 C for producing lead wires in integrated circuits. This alloying of the gold with slight quantities of rare earth metals or yttrium has markedly better strength and elongation performance at heating temperatures up to 500.degree. C., without any substantial change in other properties of the gold, such as hardness, chemical resistance, or electrical resistance.
Gold and rare earth metal alloys for bonding wires are also described in German Patent Disclosures DE 32 37 385 A (U.S. Pat. No. 4,885,135) and DE 39 36 281 A (U.S. Pat. No. 4,938,923), Japanese Patent Disclosure JP 6-112258 A, and European Patent Disclosures EP 0 743 679 A and EP 0 761 831 A.
DE 32 37 385 A relates to a fine gold alloy wire with high tensile strength, comprising a gold alloy with 0.0003 to 0.01 weight % of rare earth metal, especially cerium, and optionally germanium, beryllium and/or calcium in addition.
DE 39 36 281 A describes a gold wire for connecting a semiconductor device, comprising high-purity gold alloyed with slight quantities of lanthanum, beryllium, calcium, and elements from the platinum group, especially platinum and/or palladium.
The bonding wire known from JP 6-112258 A, reported in Chemical Abstracts, Vol. 121, 89287m, comprises a gold alloy with from 1 to 30% of platinum and 0.0001 to 0.05% of scandium, yttrium and/or rare earth metal, and optionally 0.0001 to 0.05% of beryllium, calcium, germanium, nickel, iron, cobalt, and/or silver.
In EP 0 743 679 A, a bonding wire of a gold and rare earth metal alloy containing platinum is also proposed. The alloy comprises gold and slight quantities of platinum (0.0001 to 0.005 weight %), silver, magnesium and europium, and can also contained cerium, for example, in a quantity of from 0.0001 to 0.02 weight %.
In EP 0 761 831 A, a fine wire comprising a platinum-and/or palladium-containing gold and rare earth metal alloy is described. The alloy comprises 0.1 to 2.2 weight % of platinum and/or palladium, 0.0001 to 0.005 weight % of beryllium, germanium, calcium, lanthanum, yttrium and/or europium, the remainder being gold. The wire is produced by melting the elements forming the alloy in a crucible, with cooling from bottom to top of the alloy melt in the crucible to obtain a casting (ingot), and ensuing rolling, drawing and annealing. It has an elongation of 3 to 8% and a Young modulus of 6800 to 9000 kgf/mm.sup.2.
From JP 52-051867 A, bonding wires of gold and 0.004 to 0.5 weight % of at least one of the metals in the group comprising nickel, iron, cobalt, chromium and silver is known. The bonding wires, with a diameter of 30 .mu.m, have good bonding properties and--compared with bonding wires of pure gold--improved strength. Nickel in a quantity of 0.004 weight %, at 6% elongation produces a strength of 13 kg/mm.sup.2 (130 N/mm.sup.2), and in a quantity of 0.5 weight % at 14% elongation produces a strength of 24 kg/mm.sup.2 (240 N/mm.sup.2). Higher quantities of nickel are thought to reduce the mechanical properties; for a bonding wire of a gold alloy with 0.6 weight % of nickel at an elongation of 5%, a strength of then only 10 kg/mm.sup.2 (100 N/mm.sup.2) is for instance stated. The production of the bonding wires is not described in JP 52-051867 A.
In East German Patent Disclosure DD 201 156, gold/silver alloys for bondable microwires are proposed that as additives contain copper, nickel and/or cobalt in concentrations of .ltoreq.5 mass % and iron, aluminum, palladium, platinum, antimony, bismuth, germanium, and arsenic as typical contaminants (not above 100 ppm). The alloys are melted in the vacuum induction furnace and cast to ingots. The subsequent extrusion of the ingots is followed by cold forming to the final diameter (25 to 30 .mu.m) with suitable heat treatments.
Gold/nickel alloys are also known for other purposes. For instance, Published, Examined German Patent Application 1 169 140 teaches the use of a gold/nickel alloy with 1 to 20 weight % of nickel as material for producing weak-current contacts for circuits with self-induction in the range from 10.sup.-7 to 10.sup.-4 Henry. To raise the temperature of recrystallization, the gold/nickel alloy can also contain silver, platinum, palladium, zirconium, copper, cobalt, iron, chromium and/or manganese.